Inkjet printing has gained popularity in a number of applications. One of the growing printing applications is printing of billboards, banners and point of sale displays. The ink-jet printing process involves manipulation of droplets of ink ejected from an orifice or a number of orifices of a print head onto an adjacent print substrate. Paper, vinyl, textiles, fabrics, and others are examples of print substrates. An ink-jet print head consists of an array or a matrix of ink nozzles, with each nozzle selectively ejecting ink droplets. Relative movement between the substrate and the print head enables substrate coverage and image creation. Each ink droplet comprises an image (picture) element, or “pixel.” For the simplicity of explanation the term “print head” will be used for both single print head and a plurality or print heads organized on a common mechanical structure.
Good print quality requires printing resolution higher than the native spacing of nozzles of most commercially available print heads. In order to cover the substrate with the desired print resolution a single print head scans the substrate in a reciprocating type of movement a number of times or passes. Such multi pass printing method contributes to print quality and provides a better redundancy, since different nozzles participate in printing sections of the same line when scanning the substrate in a reciprocating type of movement.
A majority of billboards and banners having relatively large dimensions are printed on flexible substrates. Roll-to-Roll (R2R) printing machines are typically used for printing on flexible substrates. One of the drawbacks of the Roll-to-Roll printing machines is the low accuracy of the relative movement between such a wide flexible substrate and the print head. When pulled/moved flexible substrate easy stretches and deforms and accordingly changes its dimensions. This makes small, comparable with the printing resolution incremental movement of flexible substrate with accuracy of few microns nearly impossible.